NFC has a range of around 5cm and has nothing to do with how AirTags work for tracking purposes. Do you really think AirTags only update their location when someone with an iPhone comes over to intentionally scan it?
Even if you bury the AirTag in the middle of the luggage, it will still be trackable, but NFC will absolutely not come even close to reaching it.
They’re not going to have off the shelf equipment capable of locating an AirTag quickly enough to matter even if they can tell there are AirTags somewhere in the general vicinity of the luggage area. That’s just not how any of this works.
Whether the rule itself is ridiculous or not, as others have pointed out, the main benefit seems to be that they can tell customers to stop bothering them about luggage that they’ve lost.